Long term evolution (“LTE”) of the Third Generation Partnership Project (“3GPP”), also referred to as 3GPP LTE, refers to research and development as part of an ongoing effort across the industry aimed at identifying technologies and capabilities that can improve systems such as the universal mobile telecommunication system (“UMTS”). The goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards.
The evolved universal terrestrial radio access network (“E-UTRAN”) in 3GPP includes base stations providing user plane (including packet data convergence protocol/radio link control/medium access control/physical layers) and control plane (including radio resource control/packet data convergence protocol/radio link control/medium access control/physical layers) protocol terminations towards wireless communication devices such as cellular telephones. A wireless communication device or terminal is generally known as user equipment (“UE”). A base station (“BS”) is an entity or network element of a communication system or network often referred to as a Node B or an NB. Particularly in the E-UTRAN, an “evolved” base station is referred to as an eNodeB or an “eNB”.
A current topic under discussion in the wireless industry relates to enhanced support of small cell deployment and operation, which may include, for example, the identification and evaluation of the benefits of UEs having dual connectivity to, for example, macro and small cell layers served by different carriers or, in some instances, the same carrier, and furthermore, for which scenarios dual connectivity may be feasible and/or beneficial. Additionally, another topic may include the identification and evaluation of potential architecture and protocol enhancements for scenarios involving UEs configured for dual connectivity in order to minimize core network impacts.
For example, in a recent agreement, two main user plane (UP) architectures considered as way forward in case of dual connectivity, (e.g., a first architecture not having a split bearer, such as “1A” and a second architecture having a split bearer, such as “3C”, each of which will be discussed later). Different architecture alternatives may be also different configuration options and they may be used simultaneously (for different bearers). However, unresolved problems may include, for example, with dual connectivity, a UE may be connected to two eNBs simultaneously (e.g., a master eNB (MeNB) and a secondary eNB (SeNB), each of which will be described later). Having a UE connected to two eNBs simultaneously may result in a situation where it is unclear, in some cases, as to which eNB the UE should transmit PHR report. In some embodiments, how the network (NW) handles uplink (UL) scheduling of the UE may also be unresolved. This invention could apply to other UP architectures for dual connectivity as well, both for bearer split and no bearer split.
TS36.321 of the 3GPP specification specifies PHR procedure, but such procedure may not be at least in some parts applicable to dual connectivity cases, such as where UEs may be connected to two eNBs simultaneously.
In regards to a PHR for dual connectivity, it has been suggested that the PHR related timers and parameters may be independently configured for each medium access control (MAC) entity, the PHR may include power headroom (PH) information of all activated cells for a user equipment (UE), and in dual connectivity, if a PHR triggering event occurs in a MAC entity, the PHR may be triggered only in the corresponding MAC entity. Furthermore, when a PHR triggering event occurs, it has been suggested that the UE triggers one PHR in corresponding MAC entity, or when a PHR triggering event occurs, the UE triggers the PHR in both MAC entities.
As such, a power headroom report (PHR) would be triggered when one of the following events occur: (a) pathloss difference according to a threshold, namely, dl-PathlossChange which sets the change in measured downlink pathloss and the required power back-off due to power management, or (b) expiration of a periodic timer, namely, periodicPHR-Timer. However, these two triggering events may be different in nature. The change of DL pathloss may indicate a channel condition change which may be likely to affect also uplink (UL) power headroom, whereas a periodic report may be sent without any change in power headroom.
In the context of dual connectivity, each Master Cell Group (MCG) and Secondary Cell Group (SCG) may have their own timers and pathloss thresholds that may trigger the PHR. As such, for each MAC entity, a PHR may be triggered, provided the dl-PathlossChange or periodicPHR-Timer occur.
It has also been suggested that (1) a pathloss change of more than dl-PathlossChange dB for at least one activated Serving Cell of an eNB may trigger a PHR to both eNBs; and (2) ProhibitPHR-Timer and PeriodicPHR-Timer may be configured and maintained independently for each of two MAC entities, ensuring both E-UTRAN Node B (eNB) may receive a PHR report.
However, the PHR may not necessarily be sent when it is triggered. Instead there may be some delay, due to, for example, the PHR not triggering Scheduling Request (SR). The PHR instead may be sent when UE otherwise obtains UL allocation next time (e.g. when there is a measurement report or user data to be transmitted). Therefore, using a single reference may be problematic because the reference may be out of date for one of the MACs leading to a PHR not being triggered even though there has been substantial change in pathloss.